This invention relates to a leveling rod for determining whether a point in question is higher or lower than a bench mark elevation and measuring how high or how low the point is relative to the benchmark elevation. The invention is particularly applicable for use in combination with laser beam level instruments used in surveying. One such instrument is described in U.S. Pat. No. 4,221,483 issued to Spectra--Physics, Inc. of Mountain View, Calif. The complete disclosure of this patent is incorporated herein by reference.
A conventional laser beam level instrument is mounted on a tripod and operates by projecting a rotating laser beam in a horizontal plane over an area to be surveyed. The laser beam is detected by a small portable electronic receiver slidably mounted to an elongated rod held upright by the surveyor. When the receiver is near horizontal alignment with the plane of the rotating laser, the receiver audibly beeps intermittently and an LCD arrow is displayed to indicate to the user whether the receiver needs to be moved up or down to achieve alignment. When the receiver is in horizontal alignment with the plane of the rotating laser beam it emits a continuous audible beep indicating this condition to the user.
A common prior art method requires the surveyor to note the point on the rod where the receiver beeps continuously while the base of the rod is on a benchmark elevation. The surveyor then places the base of the rod at a point in question and slides the receiver along the rod vertically as required to cause the receiver to beep continuously. The surveyor must then calculate the distance from the present location along the rod to the point representing the benchmark elevation and determine whether that distance indicates a measurement higher or lower then the bench mark elevation. This common prior art technique is time consuming and susceptible to miscalculations.
Another prior art technique involves using a grade rod described in U.S. Pat. No. 5,687,486 issued to Dennis Eugene Foltz and assigned to Earnhardt Equipment Company. The complete disclosure of this patent is incorporated herein by reference. This grade rod provides for determining, how high a point in question is above a bench mark elevation. The grade rod of this type has several drawbacks. Namely, the grade rod mentioned above does not provide any means for surveying a point that is below the bench mark elevation. Secondly, the tripod must be positioned at the bench mark elevation. Thirdly, the grade rod mentioned above will only survey relatively flat areas having 1 foot or less grade variation. Finally, the scale appears out of the top of the rod making it difficult to read.
The present invention speeds and simplifies the process by providing a telescoping leveling rod with a graduated scale for easily determining at a glance whether a point is higher or lower than a bench mark elevation and precisely measuring how high or how low the point in question is relative to the bench mark elevation. The present invention also provides for easily exchangeable bottom units, enabling the surveyor to utilize a longer bottom unit while checking the grade in the bottom of a ditch or similar applications. The present invention provides for surveying areas having up to 3 feet in grade variation.